Semiconductor modules for high power applications can comprise a housing and semiconductor chips sealed inside the housing. The housing has side walls, and the housing is closed on one side of the side walls by a base plate, on which the semiconductor chips are arranged. The housing is closed on the opposite side with a lid. In the housing, electrically insulating silicone gel filler is inserted, thus covering the chips. The lid, together with the packaging resin, seals the housing from the top. Typically, electrical terminals for electrically contacting the chips are soldered on the base plate. The terminals lead from the base plate through the gel, the hardened resin and the lid.
For manufacturing, the gel is filled into the housing at room temperature and is cured at an enhanced temperature, e.g., at about 125° C. A packaging resin is filled and cured on the gel filler. The resin is also cured at an enhanced temperature, e.g., at about 125° C. Therefore, the gel is thermally expanded when filling in the resin, and the gel shrinks when the module cools down. As the gel sticks to the resin, cracks emerge in the gel. These cracks can lead to partial discharge, thereby damaging or even destroying the module.
JP 10-233472 shows a semiconductor device module with means to reduce such cracks. This module comprises a housing with side walls. One side of the side walls are closed by a base plate, and the opposite side are closed with a lid. Semiconductor chips are arranged on the base plate. In the housing, silicone gel filler is inserted, thus covering the chips. A packaging resin is filled and cured on the gel filler. The lid, together with the packaging resin, seals the housing from the top. The housing has an L-shaped projection extending from the side walls into the housing. The projection is open to the gel filler, thus forming a space within the housing which is completely sealed against the surrounding. If the gel is expanded due to heat, excess pressure is produced in the air-filled space by the expanding gel and the gel presses against the lid and the packaging resin.